HOSTED BY Available online at www.sciencedirect.com ScienceDirect Natural Gas Industry B 2 (2015) 181e184 www.elsevier.com/locate/ngib Research article Application of zipper-fracturing of horizontal cluster wells in the Changning shale gas pilot zone, Sichuan Basin Qian Bin, Zhang Juncheng*, Zhu Juhui, Fang Zeben, Kou Shuangfeng, Chen Rui Downhole Service Company, CNPC Chuanqing Drilling Engineering Co., Ltd., Chengdu, Sichuan 610051, China Available online 1 September 2015 Abstract After several years of exploration practices in the Changning-Weiyuan national shale gas pilot zone, the industrial production has been achieved in a number of vertical and horizontal wells completed by SRV fracturing, and a series of independent shale gas reservoir stimulation technologies have come into being. Next, it is necessary to consider how to enhance the efficiency of fracturing by a factory-mode operation. This paper presents the deployment of Changning Well Pad A, the first cluster horizontal shale gas well group, and proposes the optimal design for the factory operation mode of this Pad according to the requirements of wellpad fracturing stimulation technologies and the mountainous landform in the Sichuan Basin. Accordingly, a zipper-fracturing mode was firstly adopted in the factory fracturing on wellpad. With the application of standardized field process, zipper operation, assembly line work, staggered placement of downhole fractures, and microseismic monitoring in real time, the speed of fracturing reached 3.16 stages a day on average, and the stimulated reservoir volume was maximized, which has fully revealed how the factory operation mode contributes to the large-scale SRV fracturing of horizontal shale gas cluster wells on wellpads in the aspect of speed and efficiency. Moreover, the fracturing process, operation mode, surface facilities and post-fracturing preliminary evaluation of the zipper-fracturing in the well group were examined comprehensively. It is concluded from the practice that the zipper-fracturing in the two wells enhanced the efficiency by 78% and stimulated reservoir volume by 50% compared with the single-well fracturing at the preliminary stage in this area. © 2015 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Sichuan Basin; Changning block; Shale gas; Horizontal well; Well cluster; Factory; Stimulation; Zipper-fracturing 1. Introduction the field test of horizontal well cluster “zipper-fracturing” has been conducted to further explore an efficient factory gas Shale gas reservoirs, with ultra-low porosity and low development mode [5]. The successful zipper-fracturing of a permeability, cannot be recovered economically without hy- horizontal well cluster on well pad A in Changning marks a draulic fracturing [1,2]. In 2009, the first shale gas vertical well fracturing technology leap from vertical wells to horizontal produced industrial gas flow after fracturing, unveiling the wells to factory fracturing of horizontal well cluster. Shale gas prelude of the shale gas exploration and development in the reservoir fracturing is shifting from single horizontal well multi- Sichuan-Chongqing area [3]. After several years of exploration stage fracturing to factory horizontal well cluster fracturing. It practices in the Changning-Weiyuan national shale gas pilot can be predicted that horizontal well cluster combined with zone, the industrial gas production has been achieved in a “factory” fracturing will gradually become the mainstream number of vertical and horizontal wells completed by SRV technology in shale gas development. fracturing, and a series of independent shale gas reservoir stimulation technologies have been developed [4]. On this basis, 2. Overview of cluster horizontal wells * Corresponding author. E-mail address: [email protected] (Zhang JC). Pad A is the first “factory” test wellpad in the Changning- Peer review under responsibility of Sichuan Petroleum Administration. Weiyuan national shale gas pilot zone in the Sichuan Basin, http://dx.doi.org/10.1016/j.ngib.2015.07.008 2352-8540/© 2015 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 182 Qian B. et al. / Natural Gas Industry B 2 (2015) 181e184 Table 1 continuous sand-supply, integrated wireline bridge running Basic information of Pad A. and cluster perforation, multi-stage fracturing, microseismic Well Well spacing (m) True vertical Horizontal Fracturing monitoring, coiled tubing drilling, and flowback fracturing depth (m) section stages fluid recycling, have formed a complete set to match with the length (m) factory fracturing [6]. Well 1 300 m away from Well 2 2491 1000 12 Well 2 / 2475 1000 12 3.2. “Zipper-fracturing” operation mode Well 3 400 m away from Well 2 2465 1000 8 The “zipper-fracturing” operation mode was adopted in the two horizontal wells on Changning Pad A, in which fracturing operation and integrated wireline bridge running and cluster perforation were simultaneously conducted in two different wells on the same wellpad in an alternate manner and seamless transition (Fig. 1). Meanwhile, microseismic monitoring was conducted in another well, and then this monitoring well was fractured solely (Fig. 2). The specific operating procedures are as follows: ① a set of fracturing equipment was used to implement zipper-fracturing in Well 1 and Well 2; ② wireline operation equipment took turns to implement bridge running and packer setting operations; ③ bridge drilling operation was conducted in Well 1 and Well 2 when Well 3 was fractured, and then bridge drilling operation was conducted in Well 3; and ④ blowout and flowback were started immediately after the bridges were drilled through in one well, till all the three Fig. 1. Schematic diagram of zipper-fracturing operation mode on Pad A. wells were all brought to flowback. and also the first horizontal wellpad deployed after the 3.3. “Zipper-fracturing” ancillary surface facilities completion of vertical exploratory wells and horizontal appraisal wells. It is drilled to the target Silurian Longmaxi Major surface facilities in “zipper-fracturing” operation Formation. A total of 6 horizontal wells in two rows are include fracturing equipment, sand blending equipment, deployed on the wellpad. As is planned, Well 1, Well 2 and continuous mixing equipment, coiled tubing equipment, and Well 3 in the updip direction will be drilled, and these wells surface flowback equipment, as well as auxiliary equipment will be fractured and tested before production (Table 1). such as water supply equipment, fluid tanks, sand tanks, and acid tanks. In addition, field continuous refueling equipment 3. Field application of “zipper-fracturing” has been developed to guarantee continuous operation of field equipment, special multi-channel wellheads were installed to 3.1. Fracturing technology meet long-time high pumping-rate requirement of fracturing operation, and the “zipper-fracturing” operation was con- Considering the ultra-low porosity and low permeability of ducted under the unified command of the first domestic “gas shale gas reservoirs, the SRV fracturing technology charac- factory” fracturing command center (Fig. 3). terized by “large-volume, high-pumping-rate, low proppant Since multiple operations and cross-operations were concentration, slick water slug injection” has been developed involved in the “zipper-fracturing” operation, the surface fa- to increase fracture-reservoir contact area and generate com- cilities were arranged according to different function areas, plex fracture network. In addition, auxiliary technologies and both operating convenience and safety were taken into including large-volume fluid storage, continuous liquid-supply consideration in the surface facility arrangement. A three-level at high pumping-rate, fracturing fluid continuous mixing, water supply mode of water source-water pit -transiting water Fig. 2. Flow of zipper-fracturing operation. Qian B. et al. / Natural Gas Industry B 2 (2015) 181e184 183 Fig. 3. The “zipper-fracturing” operation site. tank was used in ground water supply, three water pits in 4. “Zipper-fracturing” evaluation adjacent wellpads were uniformly allocated to guarantee water supply of the “zipper-fracturing” operation. In the “zipper-fracturing” operation of Pad A, obvious Fracturing equipment consists of sand fracturing truck sets instantaneous shut-in pressure differences were observed in and bridge-running truck sets. The sand fracturing truck set the fracturing operation of each stage in Well 1 and Well 2. with water horsepower of 38,000 hp (1 hp ¼ 735.499 W) was The pressure and fracture propagation of three wells were arranged in a streamline to reduce pipe abrasion during long- monitored in real time by pressure monitoring and micro- time high-pressure pumping operation. The two truck sets seismic monitoring. According to the operation pressures were connected to different processes that made fast switch and micro-seismic monitoring, sign of fracture connection has and pressure isolation possible, which can improve operation not been found in the subsequent stages (Fig. 4). efficiency and reduce high-pressure risk in cross-fracturing. The micro-seismic monitoring results show that artificial hydraulic fractures are mainly controlled by geostress. 3.4. Results of the “zipper-fracturing”